A widow is a woman whose husband has died. A man whose wife has died is a widower. The state of having lost one's spouse to death is termed widowhood or (occasionally) viduity. The term "widow" is less frequently applied to a surviving husband in a gender-neutral manner, and is sometimes applied to a woman or man whose unmarried life partner has died.

The social status of widows has been an important social issue, particularly in the past. In families in which the husband was the sole provider, widowhood could plunge the family into poverty, and many charities had as a goal the aid of widows and orphans (often, not children without parents, but children without a contributing father). This was aggravated by women's longer life spans, and that men generally marry women younger than themselves.

However, in some patriarchal societies, widows were among the most independent women. A widow sometimes carried on her late husband's business and consequently accorded certain rights, such as the right to enter guilds. More recently, widows of elected officials have been among the first women elected to office in many countries (e.g. Imelda Marcos).

There were implications for sexual freedom as well; although some wills contained dum casta provisions (requiring widows to remain unmarried in order to receive inheritance), in societies preventing divorce, widowhood permitted women to remarry and have a greater range of sexual experiences. The Wife of Bath in Geoffrey Chaucer's Canterbury Tales refers to having been widowed five times, permitting her greater sexual experience.

In some other cultures, widows are treated differently. For instance, in India there is often an elaborate ceremony during the funeral of a widow's husband, including smashing the bangles, removing the bindi as well as any colorful attire, and requiring the woman to wear white clothes, the colour of mourning. Earlier it was compulsory to wear all white after the husband was dead, and even Widow burning (sati or suttee) was practiced sometimes. However in modern day culture this has gradually given way to wearing colored clothing.

In other cultures, widows are required to remarry within the family of their late husband; see widow inheritance. This started as a custom to ensure that no widow could be kicked out of her home and face a life without financial provision, but it can also be used to keep money within the family. In addition, it is an important factor in the transmission of HIV within certain communities, e.g. the Luo, and is being challenged on human rights grounds.